The retroviral oncogene, v-fms, was acquired by genetic recombination between a filine leukemia virus (FeLV) and proto-oncogene sequences (c-fms) of normal cat cells. The v-fms gene is found in only one strain of feline sarcoma virus (FeSV) and encodes a transforming glycoprotein of unknown function. The product of the c-fms gene has not been identified, nor has its relationship to the viral transforming protein been elucidated. This proposal describes the detailed characterization of the v-fms-coded glycoprotein, defines the first steps in identifying the product of the cellular proto-oncogene, and attempts to clarify the role of these proteins in malignant transformation. Using the recently determined nucleotide sequence of a biologically active clone of FeSV DNA, we propose to place site-directed mutations in the v-fms gene. In particular, mutations will be directed to (i) limited regions of the v-fms gene which show unexpected homology to v-onc genes of the tyrosine kinase gene family, and to (ii) signal sequences which are presumed to play a role in the subcellular localization of the transforming glycoprotein. The transforming activity of altered genes will be assayed by DNA transfection onto cultured cells. Cotransfection with dominant selectable markers will be used to isolate nontransforming variants whose encoded products will be biochemically compared to those of the wild type transforming gene. The induced biochemical alterations in the v-fms gene product will be correlated with the topology of the protein and its transforming activity. In parallel studies, genomic and cDNA clones of the c-fms gene will be used to predict the primary structure of its product, thereby facilitating its identification and characterization. Recombinant DNA molecules between c-fms and v-fms will be prepared in an effort to activate the latent transforming potential of the cellular proto-oncogene. It is anticipated that a detailed characterization of domains in the v-fms-coded glycoprotein important in post-translational processing, intracellular transport, and transformation will provide the basis for activating the cellular proto-oncogene and determining its function. The latter studies will emphasize the structure and expression of the human c-fms proto-oncogene and its potential role in cancer.